There are various types of standard television signals such as an NTSC signal, a high definition television signal, and a PAL signal, which are interlaced scan video signals (i.e., interlaced video signals). A television signal such as an NTSC signal or a high definition television signal is an interlaced signal of 60 fields (i.e., 30 frames) per second, whereas a television signal such as a PAL signal is an interlaced signal of 50 fields (i.e., 25 frames) per second. Accordingly, when signals generated from a cinema film, computer graphics, or the like are converted to a television broadcast format to broadcast a program or are converted to a video package format, it is required to convert the signals having frame frequencies to the interlaced signals for television broadcast of 60 fields or 50 fields per second. This conversion is referred to as “telecine conversion”.
A cinema film is photographed in the form of 24 frames per second. When telecine conversion from a cinema film signal to an interlaced signal of 60 fields per second is performed, it is necessary to perform 2-3 pull-down conversion, in which the first frame (or an odd-numbered frame) is converted to two fields and the second frame (or an even-numbered frame) is converted to three fields, and the same field as the field previous by two fields is repeated once every five fields. Through the 2-3 pull-down conversion, a video signal of 24 frames per second can be converted to an interlaced signal of 60 fields per second. This interlaced signal is a video signal subjected to 2-3 pull-down telecine conversion, which is referred to as a “2-3 pull-down signal”. In the telecine conversion, 3-2 pull-down conversion may be performed in some cases so that the first frame is converted to three fields and the second frame is converted to two fields. However, processing of the 3-2 pull-down conversion is substantially the same as processing of the 2-3 pull-down conversion. Thus, in the present application, explanation in connection with 2-3 pull-down conversion includes not only a case of the 2-3 pull-down telecine conversion but also a case of the 3-2 pull-down telecine conversion.
Further, when a telecine conversion from a signal of a cinema film to an interlaced signal of 50 fields per second is performed, 2-2 pull-down conversion is carried out so that 25 frame video signals are generated by allocating a one-frame video signal of a cinema film to one frame of an interlaced signal and displaying twice only one frame of the cinema film, once per second, and each frame is composed of two fields. As a result, a video signal of 24 frames per second can be converted to an interlaced signal of 50 fields per second.
Furthermore, with respect to a video signal such as an animation signal created by computer graphics or a promotion video signal, a 2-2 pull-down conversion is carried out so that an original video signal of 30 frames-per second is created, one frame of the created original video signal is allocated to one frame and each frame is composed of two fields. Through the 2-2 pull-down conversion, a video signal of 30 frames per second can be converted to an interlaced signal of 60 fields per second. The interlaced signal of 50 fields per second converted from the video signal of 24 frames per second and the interlaced signal of 60 fields per second converted from the video signal of 30 frames per second, are video signals subjected to 2-2 pull-down telecine conversion. Thus, each of these interlaced signals is referred to as a “2-2 pull-down signal”.
In these years, when an interlaced television signal is displayed with a high picture quality, the interlaced signal is converted to a progressive scan signal (progressive signal). This conversion is referred to as “I/P conversion”. In I/P conversion, motion adaptive I/P conversion is generally known. In motion adaptive I/P conversion, interpolation (interfield interpolation) is performed by adding picture elements of the corresponding scan line of time-adjacent fields when a video picture is a still picture, and that interpolation (intrafield interpolation) called “motion adaptive I/P conversion” is performed by generating an interpolation signal with use of picture elements of adjacent scan lines in the same field when a video picture is a motion picture. Moreover, in I/P conversion, whether or not a video signal to be processed is a video signal subjected to telecine conversion, which is a 2-3 pull-down signal or a 2-2 pull-down signal and is referred to as a “telecine video signal”, is detected, and a phase (a direction of each of fields converted from the same frame) of the pull-down signal is detected. This detection processing is referred to as “telecine detection”. The telecine video signal is restored to a progressive signal before the telecine-conversion with use of a top field and a bottom field converted from the same frame in accordance with the detected phase of the pull-down signal, and then converted to a progressive scan video signal. Further, I/P conversion of a telecine video signal is referred to as “telecine interpolation”.
In a conventional video signal processing apparatus which detects a telecine video signal and performs I/P conversion of the telecine video signal, there is proposed an apparatus which detects a difference between a field and another field earlier by one frame (i.e., earlier by two fields) and another difference between a field and another field earlier by one field (i.e., an adjacent field), and determines a sequence of a 2-3 pull-down signal or a sequence of a 2-2 pull-down signal in accordance with a repetitive period of each field included in a result of detection of the differences, thereby performing the telecine interpolation processing (e.g., see Patent Document 1).
In the case of the 2-3 pull-down signal, the same field as the field earlier by two fields is repeatedly converted once every five fields. Therefore, a still picture field, in which difference information between a field and another field earlier by one frame becomes zero or not larger than a predetermined value, is present once every five fields. Thus, when the apparatus determines a sequence of the 2-3 pull-down signal, the apparatus performs telecine detection by utilizing such a characteristic that a difference between two fields at an interval of one frame has a repetitive period of five fields.
In the case of the 2-2 pull-down signal, one frame is converted to two fields, and a difference between adjacent fields becomes zero or not larger than a predetermined value once every two fields. Thus, when the apparatus determines a sequence of the 2-2 pull-down signal, the apparatus performs telecine detection by utilizing such a characteristic that a difference between fields has a repetitive period of two fields.
Further, there is proposed an apparatus which detects a difference between adjacent fields to perform telecine detection and which determines a sequence using a difference between a field signal and an intrafield interpolation signal to prevent erroneous detection in the telecine detection, thereby performing I/P conversion (e.g., see Patent Document 2).
Furthermore, there is proposed an apparatus which generates a matching signal indicative of the matching in accordance with an intrafield interpolation signal of the current field and a difference between fields before and after the current field and mixes signals of the fields before and after the current field using the matching signal, thereby performing telecine interpolation processing (e.g., see Patent Document 3).
Patent Document 1 is Japanese Patent Application Kokai (Laid-Open) Publication No. 2003-78926 (FIG. 1 to FIG. 4),
Patent Document 2 is Japanese Patent Application Kokai (Laid-Open) Publication No. 2004-96223 (FIG. 2), and
Patent Document 3 is Japanese Patent Publication No. 3389984 (FIG. 1).